1. Technical Field
The present invention relates to a quantum interference device, an atomic oscillator, an electronic device, and a moving object.
2. Related Art
As an oscillator having a highly accurate oscillation characteristic for a long term, there is known an atomic oscillator that oscillates on the basis of energy transition of atoms of alkali metal such as rubidium or cesium.
In general, the operation principle of an atomic oscillator is roughly divided into a system utilizing a double resonance phenomenon by light and a microwave and a system utilizing a quantum interference effect (Coherent Population Trapping (CPT)) by two kinds of light having different wavelengths. However, in recent years, the atomic oscillator utilizing the quantum interference effect is expected to be mounted on various apparatuses because the atomic oscillator can be further reduced in size than the atomic oscillator utilizing the double resonance phenomenon.
For example, as disclosed in U.S. Pat. No. 6,320,472 (Patent Literature 1), the atomic oscillator utilizing the quantum interference effect includes a cell (an atomic cell) encapsulating gaseous alkali metal, alight source that emits a resonance light pair for causing the alkali metal in the cell to resonate, and a photo detector that detects the resonance light pair transmitted through the gas cell. The atomic oscillator causes an electromagnetically induced transparency (EIT) in which, when a frequency difference between two kinds of resonance light is a specific value, both of the two kinds of resonance light are transmitted without being absorbed by the alkali metal in the gas cell, detects an EIT signal, which is a steep signal generated according to the EIT, with the photo detector, and uses the EIT signal as a reference signal.
As the light source, in general, a surface emitting laser that receives the supply of a bias current and emits light is used. Alight emitting element such as the surface emitting laser has a characteristic that a light emission wavelength changes according to the bias current and has an aging characteristic in which, even if the bias current is fixed, the light emission wavelength changes with time (gradually over a long period). Therefore, the atomic oscillator described in Patent Literature 1 controls the bias current supplied to the light source to fix the light emission wavelength.
However, in the atomic oscillator described in Patent Literature 1, since an emitted light amount changes according to the change in the bias current, frequency stability (in particular, long-term frequency stability) is deteriorated because of the influence of a phenomenon called light shift in which the resonance frequency of the alkali metal changes according to a change in the density of an amount of light irradiated on the alkali metal.